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Mixed-state fidelity and quantum criticality at finite temperature

2007; American Physical Society; Volume: 75; Issue: 3 Linguagem: Inglês

10.1103/physreva.75.032109

1538-4446

Paolo Zanardi, H. T. Quan, Xiaoguang Wang, C. P. Sun,

Cold Atom Physics and Bose-Einstein Condensates

We extend to finite temperature the fidelity approach to quantum phase transitions (QPTs). This is done by resorting to the notion of mixed-state fidelity that allows one to compare two density matrices corresponding to two different thermal states. By exploiting the same concept we also propose a finite-temperature generalization of the Loschmidt echo. Explicit analytical expressions of these quantities are given for a class of quasifree fermionic Hamiltonians. A numerical analysis is performed as well showing that the associated QPTs show their signatures in a finite range of temperatures.